Among those strengthening structures used when making laminated articles, it has been proposed for many years now to employ nonwovens of fibers, unidirectional sheets, in other words in which the structural filaments are arranged in a same direction, fabrics, bidirectional sheets such as, for example, warp and weft fabrics, or even combinations of such materials.
The present invention relates to an improvement made to bidirectional structures of the warp and weft fabric type.
Warp and weft fabrics have been proposed for many years now as strengthening reinforcements for laminated articles. They have the advantages of being able to be easily manufactured and of providing good mechanical properties both lengthwise and crosswise. For certain applications, however, they have certain disadvantages which result from the fact that the warp and weft threads undulate relative to each other after the weaving operation, when it is frequently desired to have reinforced pieces in which the filaments are arranged as straight and as flat as possible in a same longitudinal direction in order to form a uniform sheet or strip.
Consequently, numerous suggestions have been made for obtaining such sheets, currently referred to by the expression "unidirectional sheets".
Among the solutions, those forming the subject of French Patents 1,394,271 and 1,469,065 may be mentioned.